CASSIN VIREO 513 



above the ground at a fork in an outswaying branch of a young black oak 

 beneath a larger tree of the same kind. The bird came to the nest singing 

 loudly and, while still singing, proceeded to add material around the rim, 

 standing on one of the supporting twigs while it worked. Two automobiles 

 passed unheeded by the bird, which sang again before departing. Two 

 minutes later the vireo came again with material in its bill, sang, added 

 material to the nest, sang, and departed into the golden oaks across the 

 road. The bird seemed not at all inconvenienced by having its bill laden 

 with supplies, and, indeed, this is generally true of our song birds; move- 

 ment of the bill is not a necessity in singing. 



HuTTON Vireo. Vireo huttoni huttcni Cassin 



Field characters. — About half size of Junco; tail decidedly shorter than body. 

 Plumage nearly uniform greenish olive, only slightly darker above than below; eye 

 partially surrounded by light color; two pale bars on wing (pi. 50c). Movements 

 deliberate; does not habitually twitch or flutter wings as does Kinglet. Voice: Song 

 of male a hoarse, drawling ze^-ey, zee'-ey, zee'-ey ; and again, zi-ew, zi-ew, zi-ew ; these 

 notes intoned monotonously in long series; there is also a low harsh call note. 



Occurrence. — Fairly common resident locally in Upper Sonoran and lower Transition 

 zones on west slope of Sierra Nevada. Observed near Coulterville, about El Portal, in 

 Yosemite Valley, and at Gentrys. Lives almost exclusively in live oaks and golden 

 oaks. Solitary or in pairs. 



Four species of vireos or 'greenlets' are found in different portions 

 of the Yosemite section during the summer months, but only one, the 

 Hutton Vireo, remains in the region through the winter as well. This 

 vireo is almost exclusively an inhabitant of the live oaks and golden oaks 

 and this choice of habitat is doubtless the basis for the continuance of the 

 bird here during the winter moths. These 'evergreen' oaks furnish forage 

 in the form of insects throughout the year, as is shown by the number 

 of warblers and kinglets which resort to these trees during the colder 

 months. The Hutton Vireo, by being restricted to this type of tree, is 

 assured of food in all seasons, and does not need to migrate. 



The Hutton Vireo is the greenest of our four species. It is smaller 

 than the Cassin and the Warbling and larger than the Least Vireo, and 

 although it resembles the Cassin in possession of a light eye ring and two 

 bars on the wing (pi. 50e), its much greener coloration makes it readily 

 distinguishable from that gray and white-toned species. Its voice is abso- 

 lutely distinct from that of any of the other three. 



The Hutton Vireo bears a remarkable resemblance to the Ruby-crowned 

 Kinglet. The two species are of about the same general tone of coloration 

 and have in common a light eye ring and two light bars on the wing; but 

 the vireo is somewhat larger, has the appearance of big-headedness and has 



